Method and apparatus for demoisturizing and heating drying air for drying synthetic plastic material

Abstract

Drying air to be circulated for drying plastic material is demoistured and heated by one of two separate adsorbing treatment units. When one of the two units is engaged in adsorbing treatment of the drying air, the other unit engages in a desorbing treatment and cooling treatment for regenerating the adsorbent by the use of desorbing high temperature air passing through the unit in a direction reverse to that in which the drying air is passed through the unit. The cooling treatment of the adsorbent after the desorbing treatment is accomplished by the use of a part of the drying air.

I claim: 
     
       1. A method of demoisturizing and heating drying air to be circulated for drying synthetic plastic material held in a supply container, such as a drying hopper, comprising in combination the steps of: arranging two separated adsorbing treatment means, each means having a moisture adsorbing column filled with adsorbent;   connecting alternatively one of the two separate adsorbing treatment means to the supply container for a first predetermined period of time;   circulating the drying air through said supply container and the moisture adsorbing column of said one of the two separate adsorbing treatment means for said first predetermined period of time, so that the drying air which has demoisturized the synthetic plastic material is subjected to adsorption treatment by said moisture adsorbing column;   passing heated air through the other of the two separate adsorbing treatment means for a second predetermined period of time shorter than said first predetermined period of tiem during the above-mentioned circulating step so as to desorb moisture from the moisture adsorbing column of said other of the two separate adsorbing treatment means;   passing subsequently a part of said drying air, which has passed through said supply container and has demoisturized the synthetic plastic material, through the other of the two separate adsorbing treatment means for a third predetermined period of time prior to completion of the above-mentioned circulating step and after the above-mentioned passing step of the heated air, so that said moisture adsorbing column of said other adsorbing treatment means is cooled by said part of said drying air; and   mixing said part of said drying air which has passed through said other adsorbing treatment means with said drying air which has been subjected to adsorption treatment by said moisture adsorbing column of said one of said two separate adsorbing treatment means.   
     
     
       2. The method as set forth in claim 1, wherein said heated air is always passed through each of the two separate adsorbing treatment means in a direction reverse to that in which said drying air is passed through said each of the two separate adsorbing treatment means. 
     
     
       3. The method as set forth in claim 1, wherein said passing step of said part of said drying air through said other of the two separate adsorbing treatment means is started after completion of said passing step of said heated air through said other of the two separate adsorbing treatment means. 
     
     
       4. The method as set forth in claim 1, wherein temperature of said drying air is constantly monitored and detected prior to entering said supply container. 
     
     
       5. The method as set forth in claim 1, wherein said heated air is dissipated into the atmosphere after passing through the other of the two separate adsorbing treatment means. 
     
     
       6. An apparatus for demoisturizing and heating drying air to be circulated for drying synthetic plastic material held in a drying hopper with an air inlet and outlet comprising, in combination: first adsorbing treatment means including a first fixed adsorbing column filled with adsorbent and first heating means;   second adsorbing treatment means including a second fixed adsorbing column filled with adsorbent and second heating means;   first blower means connected to the air outlet of said drying hopper for promoting said drying air to be discharged from said drying hopper and to flow toward said first and second adsorbing treatment means in a first direction;   second blower means connectable to one of said first and second adosrbing treatment means for supplying air from atmostphere to one of said first and second adsorbing treatment means;   first valve means capable of taking first through third positions in a cyclic sequence, said first position permitting said drying air from said first blower means to be circulated to the air inlet of said drying hopper through said first adsorbing treatment means in which said drying air is demoisturized by said first adsorbing column and heated by said first heating means, said second position permitting said air from said second blower means to pass through said first adsorbing treatment means while desorbing mositure from said first adosrbing column, and said third position permitting a part of said drying air from said first blower means to be circulated toward said air inlet of said drying hopper through said first adsorbing treatment means while cooling said first adsorbing column and said first heating means;   second valve means capable of taking first through third positions in a cyclic sequence, said first position permitting said drying air from said frist blower means to be circulated to said air inlet of said drying hopper through said second adsorbing treatment means in which said drying air is demoisturized by said second adsorbing column and heated by said second heating means, said second position permitting said air from said second blower means to pass through said second adsorbing treatment means while desorbing moisture from said second adsorbing column, and said third position permitting a part of said drying air from said first blower means to be circulated toward said air inlet of said drying hopper through said second adsorbing treatment means while cooling said second adsorbing column and said second heating means; and   means for controlling the operation sequence of said first and second valve means in such a manner that while one of said first and second valve means is taking said first position thereof, the other of said first and second valve means takes said second and third position in succession.   
     
     
       7. The apparatus as set forth in claim 6, wherein said first valve means comprises at least one three-way valve disposed between said first blower means and said air inlet of said drying hopper, said three-way valve being able to take a position operating as said third position of said first valve means, and wherein said second valve means comprises at least one three-way valve disposed between said first blower means and said second adsorbing treatment means, said three-way valve being able to take a position operating as said third position of said second valve means. 
     
     
       8. The apparatus as set forth in claim 6, wherein said first valve means comprises a first three-way valve between said first blower means and said first adsorbing treatment means and a second three-way valve between said first adsorbing treatment means and said air inlet of said drying hopper, said first and second three-way valves being able to simultaneously take respective positions operating as said third position of said first valve means, and wherein said second valve means comprises a first three-way valve between said first blower means and said second adsorbing treatment means and a second three-way valve between said second adsorbing treatment means and said air inlet of said drying hopper, said first and second three-way valves being able to simultaneously take respective positions operating as said third position of said second valve means. 
     
     
       9. The apparatus as set forth in claim 8, wherein said first and second three-way valves of said first valve means are formed in a single valve assembly having a single drive means and wherein said first and second three-way valves of said second valve means are formed in another single valve assembly having a single drive means. 
     
     
       10. The apparatus as set forth in claim 9, wherein each of said two single valve assemblies comprises a fixed port defining plate, a rotatable valve plate cooperable with said fixed port defining plate, a position-indicating plate rotatable with said rotatable valve plate, and position detecting means cooperable with said position-indicating plate for controlling said single drive means. 
     
     
       11. The apparatus as set forth in claim 8, wherein said first and second three-way valves of said first valve means are mechanically interconnected with one another, and said first valve means further comprises a single drive means for commonly operating both said first and second three-way valves so as to take said first through third positions; and wherein said first and second three-way valves of said second valve means are mechanically interconnected with one another and said second valve means further comprises a single drive means for commonly operating both said first and second three-way valves so as to take said first through third positions. 
     
     
       12. The apparatus as claimed in claim 6, wherein said first and second heating means of said first and second adsorbing treatment means are used for heating said drying air demoisturized by said first and second adsorbing columns to a first preselected temperature suited for drying said synthetic plastic material, respectively, and for heating said air from said second blower means to a second preselected temperature suited for desorbing moisture from said first and second adsorbing columns, respectively. 
     
     
       13. The apparatus as claimed in claim 12, further comprising a first temperature-sensing means for detecting a temperature of said drying air prior to entering into said air inlet of said drying hopper and a second temperature sensing means for detecting a temperature of said air which has passed through one of said first and second adsorbing treatment means. 
     
     
       14. The apparatus as claimed in claim 12, wherein said first and second heating means comprise electrically powered heaters. 
     
     
       15. The apparatus as claimed in claim 6, wherein said adsorbent of said first and second adsorbing columns is synthetic zeolite.